Low-maintenance coatings, e.g., photocatalytic coatings and hydrophilic coatings, are known in the art. Photocatalytic coatings, e.g., titanium dioxide coatings, have self cleaning characteristics in that organic matter deposited on the surface of the coatings can be chemically degraded by the coatings. Generally, a thicker titanium dioxide coating is more efficient at degrading organic matter but is often very reflective. A thinner titanium dioxide coating is less reflective but may not be as efficient in degrading organic matter. Highly reflective coatings are undesirable because they are somewhat mirror like, which creates an undesirable appearance when the coating is provided on transparent substrates, e.g., window panes.
Low-emissivity coatings are also known in the art. Typically, they include one or more infrared-reflective films each positioned between two or more transparent dielectric films. The infrared-reflective films, which are typically conductive metals such as silver, gold, or copper, reduce the transmission of radiant heat through the coating (e.g., by reflecting infrared radiation). The transparent dielectric films are used primarily to reduce visible reflectance and to control other coating properties, such as color. Commonly used transparent dielectrics include oxides of zinc, tin, and titanium, as well as nitrides such as silicon nitride. Low-emissivity coatings are often designed to achieve a combination of properties tailored to meet the requirements of a particular application. The thickness of the dielectric films, for example, can be modified to achieve particular transmission, reflection, and color properties.
It would be desirable to provide both a low-maintenance coating and a low-emissivity coating on the same pane. It would be particularly desirable to provide such a pane with good balance of low-maintenance properties, thermal-insulating properties, neutral color, high visible transmission, and low visible reflectance.